1 . Field of the Invention
The present invention relates to a switching power supply, and particularly to a switching power supply used as a DC—DC converter.
2 . Related Background of the Invention
In recent years, there have been growing demands for energy saving and environmental conservation, and, as one of what reflect such demands, hybrid cars have been put into practical application. A hybrid car is a car that utilizes, as its power source, a conventional internal combustion engine and an electric motor (motor for a hybrid car) combined therein. The motor for a hybrid car is capable of recovering electric energy by performing power regeneration when the speed is reduced or the like. The regenerated power as well as power generated by utilizing outputs of the internal combustion engine are stored in a battery.
A voltage supplied from a battery is stepped down in a DC—DC converter to be distributed to on-vehicle equipment such as headlights. Moreover, the stepped down power is distributed also to the aforementioned motor for hybrid cars through an inverter. Such a DC—DC converter essentially includes: an input smoothing circuit for removing noises of an input voltage; a switching circuit for converting a direct current into an alternating current; a main transformer for stepping down a voltage; a rectifier circuit for converting an alternating current into a direct current; and an output smoothing circuit for removing noises of an output voltage. Among the circuits and the main transformer (hereinafter, referred to as “elements”), a switching circuit having a switching element such as a metal-oxide-semiconductor field-effect transistor (MOSFET), and a rectifier circuit having a semiconductor diode are heated up to have a temperature as high as a hundred and several dozen degrees Celsius when a converter is operated. Therefore, measures for releasing the heat are generally taken at least for these elements.
For example, in an electronic circuit device (switching power supply) disclosed in Japanese Patent Laid-Open No. 2000-13062, among regions in the base plate on which the aforementioned respective elements are mounted, radiator plates are provided in regions corresponding to the positions of the elements, thereby enhancing heat release from the hot elements. Note that, in this switching power supply, the heights of the elements are adjusted by positioning the radiator plates at different heights from one another.
However, with respect to the above switching power supply, although the space used for the device is reduced by adjusting the heights among the elements, there have been problems concerning the cooling capacity thereof. More specifically, in a switching power supply whose output is high enough (around 110A) for application to a hybrid car, the elements are not cooled down to a required and sufficient level only with the radiator plates attached to the elements. Thus, characteristics of the elements are deteriorated, and the elements may be broken in some cases. Therefore, in practice, a water-cooling method with a sufficient cooling capacity such as one disclosed in Japanese Patent Laid-Open 2003-08264 is adopted. That is, a method of suppressing excessive heating of the elements through the base plate is adopted. Here, radiator fins are provided on the opposite side of the element mounting surface of the base plate on which the respective elements are mounted, and coolant is flown between the radiator fins.